Theory 1.2 Flashcards
What is pulsating DC ?
- Pulsating DC (PDC) is a type of direct current (DC) that varies in magnitude but never changes direction
- DC fluctuates between zero and a peak value.
Adding any number of sine waves of the same frequency will always produce a sine wave of the same frequency with unique magnitude and phase.
TRUE OR FALSE
TRUE
Which waveform is leading/lagging ?
What is RMS ?
- Equivalent ac voltage that would deliver the same power to a load as dc voltage
- Same formula for current rms
What are the formulas for ac ohm’s law and power law. (For 100% ohmic element)
What happens when a charged capacitor is grounded at only one side ?
- no discharge occurs, direct path must exist btw the 2 plates.
What is capacitance ?
- The ratio of the electric charge on one plate to the potential difference (voltage) between the plates.
What is leakage current in capacitors?
- Is the small amount of unintended current that flows across the dielectric material when a capacitor is charged.
How do electrolytic capacitors work ?
- They use aluminium-foil plates with semi conducting chemical compound btw them.
- Dielectric = thin film of insulating material, forms on 1 set of plate through electrochemical action when dc volt is applied
- NOT used in ac applications
What happens to voltage and current during capacitor charging and discharging?
What is energy formula for capacitor ?
What is RC Time Constant ?
- RC time constant is the time it takes for the voltage across the capacitor to either charge or discharge to approximately 63.2% or 37.8% of its final value.
- Capacitor fully charges or discharges after 5 time constant ( 5 tau)
what is stray capacitance ?
- its unintentional capacitance that exists between parts of a circuit that are not supposed to act as capacitors.
- This happens due to the close proximity of conductors, like wires or circuit traces, which can cause a bit of a charge buildup between them.
What are the formulas for capacitors in parallel and in series ?
- Capacitors in parallel add up.
- Voltage limited to the capacitor with smallest volt rating
- For cap in series, total cap < smallest cap
What does the graph of AC current applied to capacitor look like.
Is power dissipated in capacitive reactance as heat or any form of energy ?
- Capacitive reactance doesn’t dissipate power, energy is alternately stored and released with each AC cycle
What is Self Resonant Frequency in capacitors ?
- It’s the frequency where the capacitor’s own inductive and capacitive properties cancel each other out.
- Beyond this point, the capacitor’s impedance starts to increase, and it behaves like an inductor.
- Defines the maximum effective frequency range of the capacitor.
What is the formula for capacitive divider ?
What is the relationship btw electromagnetic fields and stationary, moving(constant velocity) and accelerating charges ?
- Stationary Charge = electric fields surround the charge
- Moving Charge = magnetic field surround moving charge
- Accelerating Charge = kink created in electromagnetic field, electromagnetic waves radiates out.
What happens to the magnetic fields of electrons in a conductor without applied voltage?
Without applied voltage, the magnetic fields of electrons point in random directions, resulting in a net magnetic field of zero.
What occurs when a voltage is applied across a conductor in context of magnetic field?
When a voltage is applied, free electrons gain a drift component, generating a net magnetic field.
What is the direction of the magnetic field in relation to conventional current flow?
The magnetic field is perpendicular to the direction of conventional current flow and follows the right-hand rule.
What is the right-hand rule?
In the right-hand rule, your thumb points in the direction of conventional current flow, and your fingers curl in the direction of the magnetic field.
What generates the magnetic field in a permanent magnet?
- By the motion of unpaired electrons orbiting the nucleus of an atom.
What role does the lattice structure of ferromagnetic materials play?
The lattice structure fixes a large portion of atomic magnetic dipoles in a fixed direction, creating a net magnetic dipole.
How does placing a ferromagnetic material inside a solenoid affect the magnetic field?
Placing a ferromagnetic material inside a solenoid increases the magnetic field strength by aligning the core’s atomic magnetic dipoles.
How do you determine the direction of force on a positive charge in a magnetic field?
- Use your right hand
- Left hand for negative charge
What happens when a charge moves parallel to the applied magnetic field?
It experiences no force due to the magnetic field.
What is the interaction between two wires carrying current?
The net magnetic field of one wire will exert a force on the other wire and vice versa, provided the current is fairly large.
According to Faraday’s law, what induces EMF in a circuit?
EMF is directly proportional to the time rate of change of the magnetic flux through the circuit.
What are the ways EMF can be induced in a circuit?
- The magnitude of B can vary with time
- The area of the circuit can change with time
- The angle between B and the normal of A can change with time
- Any combination of these can occur.
What is the difference between an AC generator and a DC generator?
A DC generator uses a split ring or commutator for contacts, resulting in a pulsating direct current.
What is self-inductance?
Self-inductance is the phenomenon where a looped wire generates an induced EMF due to the varying current passing through it.
What does Faraday’s law of induction state regarding self-induction?
According to Faraday’s law of induction, self-induction occurs when the magnetic field through a loop grows or shrinks due to changes in current.
What is the role of self-induction in inductors?
- Used to store and release energy as current levels fluctuate in time-dependent circuits.
What happens when a switch in a circuit is closed? (In relation to self-induced EMF)
When the switch is closed, the current does not jump immediately to V/R; instead, it increases rapidly, inducing an EMF that opposes the current flow.
What is a self-induced EMF?
A self-induced EMF is the induced EMF that opposes the current flow in a circuit when the current changes.
How do inductors differ from simple circuits regarding self-induction?
Inductors are designed to generate large concentrations of magnetic flux and experience significant self-induction during changes in current.
What is the common geometry of inductors?
Inductors commonly have a looplike geometry, such as solenoids, toroids, or spiral shapes.
What is the advantage of using a magnetic core in inductors?
Using a magnetic core allows for generating higher magnetic field densities and achieving desired inductance with fewer turns of wire.
What are adjustable inductors?
Adjustable inductors are inductors whose effective coil length can be altered, typically using a slider or a slug made of different materials.
What is a ferrite bead?
A ferrite bead is a device that increases the inductance of a wire by placing it through a hollow bead, absorbing RF radiation and converting it into heat.
What is the typical application of ferrite beads?
Ferrite beads are often used on cables to prevent RF radiation (EMI) from interfering with electronic equipment.
What is the primary function of an inductor?
An inductor acts like a time-varying current-sensitive resistance, resisting changes in current.
How does an inductor behave under steady-state DC conditions?
Under steady-state DC conditions, an inductor passes current as if it were a wire.
What happens when voltage increases across an inductor?
The inductor acts like a time-dependent resistor, resisting rapid increases in current.
What occurs when voltage decreases across an inductor?
The inductor acts like a time-dependent voltage source, attempting to keep current flowing.
What is reverse and forward EMF in the context of an inductor?
- Reverse EMF is the induced EMF that points in the opposite direction of the applied voltage during an increase in current.
- Forward EMF is the induced EMF that points in the same direction as the applied voltage during a decrease in current.
What happens when an inductor is energized and de-energized suddenly?
- Electrical energy is transformed into a magnetic field, and inductive behavior affects circuit dynamics.
- The magnetic field energy is transformed back into electrical energy, affecting current flow.
What is the effect of closing a switch in an inductor, capacitor and resistor circuit?
- The lamp will light up brightly but quickly dims out due to the inductor’s high initial impedance.
- The lamp slowly builds up in brightness until it reaches maximum illumination.
- Free-electron flow is essentially instantaneous, and the brightness of the lamp remains constant.
